Miniaturized hinge constructions are used particularly in two-part mobile telephones and in various hand-held electronic devices. Such devices often comprise a base part and a top part turning in relation to it. In order to use these devices the two parts of the device are unfolded into a position, in which the parts form a certain angle between them. It is striven for that a device stays firmly in the open position when it is used and is not closed too easily. To close the device one has to direct at the turning part a force exceeding the friction and spring force resisting this movement. From the point of view of using the device, the force should not be too high nor too low. In certain cases it is also desirable to allow within certain limits an adjustable opening angle in order to arrange an ideal viewing angle in relation to the turning part for users of different height viewing the device from different levels. One of the desired features of such hinged electronic devices often is the smallest possible size. This desire generates a need to make also the hinges as small as possible. Yet the hinge constructions should endure wear well, in some cases up to 100000 times of opening and closing.
From Patent application publication FI 961587 such a hinge mechanism is known, in which a spring loaded moving part causes in a hinge that has been opened at a certain angle a force resisting its closing and preventing from opening the hinge any more. Even if the hinge is durable, it does not in all possible conditions prevent from closing the device by using the same force.
FIG. 1a shows a hinge for a portable computer according to U.S. Pat. No. 5,715,576, which allows, within certain limits, to open the display of the computer at a desired angle. Elongated and two-ended round rod 1 has at its first end been fixed to display frame 51. In the other end of the rod it has been fixed concentrically elongated and two-ended thin hinge axis 11. In the base of the hinge axis and the rod there is fixed on the axis and the rod round bushing 101, the head of which against the rod has been bevelled sharp on both its sides. The bevels end approximately in the middle of the length of the bushing. In this way it has been formed hinge axis 11 that is wedge-shaped in its base. In the frame of computer 50 it has been fixed outer bushing 2, narrowing toward the base of the hinge axis and internally tapered, in such a way that it surrounds the hinge axis co-axially. Friction piece 30 has been slipped around the hinge axis between the outer bushing and the hinge axis, which has the form of a cylinder tapering toward the base of the hinge axis. On the end of the friction piece facing the wedge shaped part of the base of the hinge axis there is a V-shaped slot that has been adapted to fit on the wedge shaped part of the base of the hinge axis. The tapered cylindrical surface of the friction piece has been adapted to follow the inner surface of the outer bushing and to generate friction on this junction to prevent it from rotating when the friction piece has been pushed toward the base of the hinge axis far enough for the bevel of the base of the hinge axis to fill the slot. In the assembly stage the outer bushing of the hinge has been placed around the hinge axis against rod 1. Friction piece 30 has been slipped around the hinge axis and been pushed into the outer bushing on the hinge axis, and spring 44 has been placed on the hinge axis. Then the spring has been compressed and fixed against the friction piece using plug 4 which has been locked to outer bushing 2.
When the display is turned to another position, the axis of the hinge fixed to the display starts to turn. The wedge in its base then turns slightly in the slot of the friction piece and causes a turning force in the slot, and because of the bevelled surface of the wedge, also a force attempting to draw the friction piece away from the base of the axis, and the friction piece moves a little axially against spring 44. At the same time, as the friction piece is drawn away from the narrower end of the outer bushing, the friction coefficient between the friction piece and the outer bushing is reduced and also the force turning the slot of the friction piece is reduced. Thus, when the display is turned, a balance is formed, wherein the force turning the slot settles on a certain level and the friction piece is slightly offset away from the base of the axis against compressing spring 44. When turning the display is ceased, the friction piece is again pressed against the base of the hinge axis as far as the spring force can push it against the tapered outer bushing and the wedge shaped part.
When the surfaces of the friction piece and outer bushing rubbing against each other become worn, the friction force preventing the hinge from turning becomes insufficient. The main part of the friction force is caused by the rubbing of surfaces between the friction piece and the outer bushing and only for a minor part by rubbing between the friction piece and hinge axis 11. When these surfaces wear, the depth of the slot limits the movement in the direction of the hinge axle of the friction piece when the bottom of the slot is pressed against the wedge shaped part. When the bottom of the slot is pressed against the wedge shaped part the slot receives the pressure caused by the spring and thence no pressure is generated between the friction surfaces, and due to it the friction between the friction surfaces disappears and the hinge no longer operates as designed. The hinge also takes up a reasonably big space.
As an additional feature it is desired of the hinge of a two-part mobile station a possibility to lead through the hinge an antenna cable from one folding part to the other, e.g. between the base part and the display part. This is necessary for example if the radio part is in the base part and it is desired to place an antenna in the other part in order to make it possible for a user to freely support the base part by its edges in his palms without needing to avoid the location of the antenna in the base part. An example of such a device is the Nokia 9000 Communicator mobile station that combines a PDA-device (Personal Digital Assistant) and a mobile station into a hinged two-part device.